CHICAGO (CBS) — If you plan to head out to cash in on the big after-Christmas sales, you’ll certainly want to pack on the layers, as bitterly cold temperatures have gripped the Chicago area.

After a Christmas that was the coldest in 13 years in Chicago, with a high of only 21, the mercury dipped below zero for the first time this winter overnight, reaching 2 below zero by 6 a.m. at O’Hare International Airport, according to the National Weather Service. Wind chills plunged to as low as 17 below zero.

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The Christmas Day high of 21 was the city’s coldest since 2004, when the high was only 19. The record for Christmas in Chicago was 5 below zero in 1983.

Tuesday’s temperatures will be even colder, reaching a high of only around 12 degrees in Chicago.

The National Weather Service has issued a wind chill advisory for Lake, Kane, McHenry, DeKalb, Boone, Ogle, and Winnebago counties until noon, as wind chills could drop to 25 below in some areas.

If you have to be outside, make sure you dress in layers, and avoid having any skin exposed to the wind and cold for a prolonged period of time. According to the National Weather Service, frostbite can set in in a matter of minutes if your skin is exposed to such cold conditions. Fingers, toes, ears, nose, and cheeks are most at risk.

Skip Roberts found himself outside early Tuesday morning, trying to give his two Chihuahuas a bathroom break. He’s not a fan of the cold, and neither are his dogs.

“It’s tough all the way around,” he said. “We go down in the Grant [Park] parking garage, and I at least give them a little walk. So, you know, it’s very difficult. It’s even cold in there.”

The bitter cold might thin out the crowds a bit at stores offering after-Christmas sales.

In Aurora, the Wal-Mart opened at 6 a.m., and was scheduled to remain open until midnight. Some analysts said the day after Christmas is the new Black Friday, as millions of people flock to stores across the U.S., looking for major sales.

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Ethel Wright, from Maywood, was determined to get a good deal on Tuesday, despite the frigid weather.

“I like getting the sales after Christmas; much cheaper, and I get my yard prepared for next year,” she said. “I’ve got to come out into the cold anyway. I’ve got to come to work.”

The pursuit of the right deal had Veronica Santillan standing outside Bath and Body Works in Aurora 20 minutes before the store opened. Temperatures below zero and a wind chill of nearly 20 below didn’t scare her away.

“Not really. We got what we needed,” she said.

According to the National Retail Federation, 47 percent of consumers say they plan to take advantage of after-Christmas sales in stores around the country.

“It’s the day after Christmas, and so I had to return something, and I want to get here and get the size that I need before everybody else gets here and takes what I need,” Lori Hampton said.

In addition to returns, Americans are expected to start redeeming about $30 billion worth of gift cards.

The cold wasn’t about to keep the Watson sisters from the mall either.

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“We’re from around here, so we’re pretty used to this, and I go to school downtown, so I’m really used to the wind chill,” she said.